An EOF analysis of the structure of the large-eddy motion in a simulated vegetation canopy

We have conducted an empirical orthogonal function (EOF) analysis of a three-dimensional velocity and scalar field within and above a forest canopy. The data we work with is the output of a large-eddy simulation (LES) over a domain composed of 288x144x100 grid elements. The EOF analysis consists of finding the sequence of orthogonal eigenfunctions and associated eigenvalues that converges optimally fast when the variance of the turbulent field is expressed as the sum of this sequence.

The analysis was applied to (i) only the vertical direction; (ii) the x-z and y-z planes; and (iii) the full three dimensions, and was formulated to include two, three or four of the variables: velocities u, v, w, and scalar c. In general, a large fraction of the total variance is captured by the first few eigenmodes. We will show examples of the "characteristic eddy" that is reconstructed from such eigenmodes.